The present invention relates to a light projecting device used by a distance measuring apparatus to measure the distance of an object from the apparatus.
Conventionally, various types of distance measuring apparatus have been proposed for cameras, video cameras and other optical equipment. One common distance measuring apparatus employs a passive distance measuring method (Phase Matching method).
A passive distance measuring method uses two sensors located on a plane and separated by a certain distance, to measure light reflected by an object. This system utilizes the ambient light to illuminate the object, and thus has low power consumption. Further, a passive system can be used to measure a distance of an object that is far away. An active system which employs a pulsed light source to illuminate an object, can only measure the distance of objects close to a light source. Thus a passive system can accurately drive the lens to focus on distant objects.
These features have made the passive distance measuring method very popular in autofocus single lens reflex cameras and zoom compact cameras.
However, the passive distance measuring method relies on a high contrast ratio between the object and background since there must be enough light reflected by the object In order to properly measure the object distance. Further, the distance of a uniformly lit object such as a wall, which has a similar brightness level across its surface, cannot be accurately determined, using a passive distance measuring method.